In contrast to WAVE, MP3 etc, MIDIs are not audio files. They contain description on how to create music, but not music itself.

The task of converting MP3 to WAVE and WAVE to MP3 is easy, there are many free software products capable of doing this. MIDI to MP3 conversion is more difficult, it is called MIDI rendering and is similar to using a synthesizer, but you can still find free products doing it.

MP3 to MIDI is another story. It's like making sheet music out of complex recording. You would need a skillful musician and pretty much time, and there's still no guarantee that you will get every note right. Done by software, it is somewhat similar to speech or handwritten text recognition, and involves complex AI algorithms. It is thus also known as music recognition. Don't expect miraculous results, especially on complex music with plenty of different instruments (simple melody using one instrument or voice is better to detect). You will also need to play with settings to get your melody the way you want it.

Based on the above considerations, programs converting WAV or MP3 to MIDI are complex and tend to be expensive. So I’d be surprised if you can find one for free, but wish you luck.